path: root/kernel
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authorOleg Nesterov <oleg@redhat.com>2015-02-12 20:59:13 +0100
committerIngo Molnar <mingo@kernel.org>2015-02-18 14:27:40 +0100
commitbc9560155f4063bbc9be71bd69d6726d41b47653 (patch)
tree9d4be1d4a9526b0b0d9e74cfb335ad696195685f /kernel
parentsched: Fix preempt_schedule_common() triggering tracing recursion (diff)
sched/completion: Serialize completion_done() with complete()
Commit de30ec47302c "Remove unnecessary ->wait.lock serialization when reading completion state" was not correct, without lock/unlock the code like stop_machine_from_inactive_cpu() while (!completion_done()) cpu_relax(); can return before complete() finishes its spin_unlock() which writes to this memory. And spin_unlock_wait(). While at it, change try_wait_for_completion() to use READ_ONCE(). Reported-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reported-by: Davidlohr Bueso <dave@stgolabs.net> Tested-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> [ Added a comment with the barrier. ] Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Nicholas Mc Guire <der.herr@hofr.at> Cc: raghavendra.kt@linux.vnet.ibm.com Cc: waiman.long@hp.com Fixes: de30ec47302c ("sched/completion: Remove unnecessary ->wait.lock serialization when reading completion state") Link: http://lkml.kernel.org/r/20150212195913.GA30430@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel')
1 files changed, 17 insertions, 2 deletions
diff --git a/kernel/sched/completion.c b/kernel/sched/completion.c
index 7052d3fd4e7b..8d0f35debf35 100644
--- a/kernel/sched/completion.c
+++ b/kernel/sched/completion.c
@@ -274,7 +274,7 @@ bool try_wait_for_completion(struct completion *x)
* first without taking the lock so we can
* return early in the blocking case.
- if (!ACCESS_ONCE(x->done))
+ if (!READ_ONCE(x->done))
return 0;
spin_lock_irqsave(&x->wait.lock, flags);
@@ -297,6 +297,21 @@ EXPORT_SYMBOL(try_wait_for_completion);
bool completion_done(struct completion *x)
- return !!ACCESS_ONCE(x->done);
+ if (!READ_ONCE(x->done))
+ return false;
+ /*
+ * If ->done, we need to wait for complete() to release ->wait.lock
+ * otherwise we can end up freeing the completion before complete()
+ * is done referencing it.
+ *
+ * The RMB pairs with complete()'s RELEASE of ->wait.lock and orders
+ * the loads of ->done and ->wait.lock such that we cannot observe
+ * the lock before complete() acquires it while observing the ->done
+ * after it's acquired the lock.
+ */
+ smp_rmb();
+ spin_unlock_wait(&x->wait.lock);
+ return true;